Internal combustion engines operating on a two-cycle principal have traditionally been arranged so that fuel is delivered into an incoming air supply. The fuel and air mixture passes into a crankcase chamber for crankcase compression, and is then delivered through a scavenge passage to a combustion chamber of the engine for combustion therein.
As is well known, in the operating cycle of a two-cycle engine, an exhaust port leading from the combustion chamber is open during at least part of the time the scavenge passage is open. Thus, exhaust along with a portion of the air and fuel charge being delivered through the scavenge port flow through the exhaust port into the exhaust system.
In this arrangement, and especially at low engine speeds, a large amount of fuel must be added to the air to compensate for the loss of fuel flowing through the cylinder and directly out the exhaust port. Supplying excessive fuel, however, is costly and can result in stalling of the engine. In addition, the quantities of fuel flowing into the exhaust may foul a catalyst positioned in the exhaust system.
As one attempt to solve the above-stated problems, some two-cycle engines have been arranged to have fuel directly injected into the combustion chamber. A fresh air charge is supplied to each combustion chamber through the crankcase and a scavenge port. Once air is supplied to the combustion chamber and the exhaust port is closed, a fuel injector injects fuel directly into the combustion chamber for mixing with the air.
This arrangement has the benefit that little of the fuel flows unburned into the exhaust system, and the amount of fuel supplied to each combustion chamber may be closely controlled. On the other hand, in order for this system to work, fuel must be supplied to the fuel injector under high pressure. In particular, a large amount of fuel must be sprayed into the combustion chamber in a short time, and in a manner which atomizes the fuel. Thus, these systems have a fuel supply which includes a fuel tank and a high pressure pump for pumping fuel from the tank and supplying it under high pressure to the fuel injector.
A problem with this arrangement arises in pressurizing the fuel from tank pressure (typically atmospheric pressure) to this high pressure by the high pressure pump. First, if a single pump is used, for the pump to create the large pressure head in the single step, its capacity must be very low and insufficient fuel may be supplied to the engine. Another problem is the introduction of large amounts of vapor into the fuel. This vapor may cause a vapor lock in the system and alters the amount of fuel which is actually delivered to the combustion chamber during a desired fuel delivery time. Thirdly, such a high pressure pump must operate at high speeds, and thus achieves high temperatures. When the fuel is hot, vapor creation within the fuel is accelerated, worsening the above-stated problems.
A fuel supply system for delivering fuel from a fuel source to a combustion chamber of an engine through a fuel injector at high pressure and without the above-stated problems is desired.